Bacillus cereus: a toxin that survives 121 °C for 30 minutes — and the hot-holding mistake

According to the FDA’s Bad Bug Book, B. cereus causes two distinct illnesses through two distinct metabolites. The diarrhoeal type is caused by a large-molecular-weight protein; the vomiting (emetic) type is associated with a low-molecular-weight compound called cereulide.

The onset times differ too: 6 to 15 hours after consumption for the diarrhoeal type, and 0.5 to 6 hours for the emetic type.

The Bad Bug Book states that cereulide is pH-stable and resistant to heat and proteases. The compound remains stable after heating at 121 °C for 30 minutes, after cooling at 4 °C for 60 days, and across a pH range of 2 to 11.

Those figures say that no kitchen process can destroy this toxin: 121 °C is autoclave temperature. The only control point is therefore that the toxin never forms — that is, closing the time-and-temperature window in which the bacterium multiplies.

The source gives the optimal growth temperature as 28–35 °C, the minimum as 4 °C and the maximum as 48 °C. Growth can occur across pH 4.9 to 9.3 and the organism tolerates a 7.5% salt concentration.

In catering that range maps directly onto service practice: products left at room temperature after cooking, cooled slowly, or not held hot enough. Because B. cereus spores survive cooking, growth does not restart from zero when the product turns warm — it restarts from the surviving spores.

The Bad Bug Book states that the presence of large numbers of B. cereus in a food (greater than 10⁶ organisms per gram) indicates active growth and proliferation of the organism and is consistent with a potential human health hazard. The counts most often associated with human illness are 10⁵ to 10⁸; the pathogenicity, however, arises from preformed toxin.

Fatal outcomes are rare but recorded: the source reports that the emetic enterotoxin has been implicated in liver failure and death in otherwise healthy individuals, and that a newly identified cytotoxin was isolated from a strain that caused a severe outbreak with three deaths.